Facing heads are primarily used for facing of workpiece surfaces to a high surface quality and for cutting during internal and external machining. In addition, there are facing heads as they are needed for example for the valve machining industry or spherical-turning heads for the axle or armature industry. Replacement attachment tools broaden the field of use of a facing head.
In a known device for holding and operating a facing head of the above-disclosed type (DE-C 2 608 930), the adjusting mechanism includes an actuator rod arranged coaxially movably with respect to the axis of rotation of the supporting body on helical tooth systems arranged on two diametrically opposite sides, the teeth which cross, however, in relationship to the direction of movement of the actuator rod have the same angle. Each of two serrated slats arranged symmetrically with respect to the actuator rod are provided on the slide and on a counterweight of the slide, which serrated slats mate with the helical tooth system on the actuator rod. The teeth on the serrated slats of the slide extend thereby in opposite direction of the ones of the serrated slats on the counterweight. In the place of the counterweight, it is also possible to provide a second slide movable in an opposite direction to the first slide. A cross-feed mechanism extending centrally through the machine spindle is needed to operate the actuator rod. The cross-feed mechanism has been constructed especially for this purpose and can be operated from the side of the tool. On the other hand, the center area of the machine spindle is occupied with a feed device for the tool in machining centers with an automatic tool replacement capability so that an additional cross-feed mechanism cannot easily be stored there. On the other hand, it would be of a great advantage, in the interest of a complete machining of workpieces in one setting, when facing heads could also be inserted into machining centers.
It is hereby conducive to use the fluid coolant existing in each machining center and circulated with a high pressure of at least 15 bar as a drive means for the cross slide.
Based on this, the basic purpose of the invention is to provide a device for holding and operating a facing head of the above-disclosed type, with which, using the coolant in particular also existing in machining centers and circulating it under pressure, a slide adjustment is assured which is reliable, also at high speeds, and suitable for continuous operation.
To attain this purpose the following combination of characteristics is suggested according to the invention:
The supporting body has two spaced chambers arranged coaxially with respect to the axis of rotation, in which chambers are arranged two pistons rigidly coupled with one another and to the actuator rod; PA1 the first of the two chambers is loadable on the one piston side with pressure fluid from the coolant channel and on the other piston side with atmospheric air; PA1 a return spring acting against the force of the pressure fluid onto the piston arrangement is provided; PA1 the second chamber is connected on both sides of the piston to a closed hydraulic circuit which contains a check valve closing in machining direction of the slide movement and opening in return direction, and a flow-control valve. PA1 Center of gravity shift of the moved masses in various stroke positions of the slide; PA1 variable speeds and thus variable centrifugal forces acting on the slide; PA1 variable load during the machining operation based on different clamping cross sections; PA1 pressure variations in the coolant system.
The division into two separate hydraulic circulating systems makes it possible that in the open coolant circulating system also more or less contaminated coolant both for the cross-slide drive and also for the cooling and chip removal in the machining area can be utilized, and that the control of the feed and return speed, for which control is important, uncontaminated fluid be used, can be carried out in a closed hydraulic circuit. Since the centrifugal forces, depending on the speed of the facing head in the slide area, must be overcome by the operating device, the slide feed must be adjusted by adaptation to the respective machining tasks from case to case through the flow-control valve in the closed hydraulic circuit. The flow-control valve contains for this purpose advantageously an externally adjustable adjusting throttle for adjusting the volume flow within the closed hydraulic circuit. It must thereby be considered that significant pressure variations can result in the hydraulic circuit, for example for the following reasons:
In order to maintain the feed speed constant independently from pressure variations, the flow-control valve contains, according to a preferred embodiment of the invention, in addition a piston manometer with which the volume flow adjusted on the adjusting throttle can be very exactly controlled. The piston manometer has advantageously an operating piston controlling the cross section of an outflow opening of the flow-control valve, loaded with the difference pressure occurring at the adjusting throttle and a compression spring acting in opening direction of the outflow opening.
The spring acting onto the piston arrangement and the check valve in the closed hydraulic circuit permit, if necessary supported by the centrifugal force acting on the slide, an automatic quick return of the slide into its initial position.
In order to avoid a loss of fluid from the coolant channel of the supporting body during a tool exchange, an initially biassed check valve is arranged on the inlet side of the coolant channel. To moreover enable a transfer of coolant to the machining area of the facing head and to simultaneously avoid a fluid escape during the exchange of the head element, a check valve is arranged on the outlet side of the coolant channel in the supporting body, which check valve prevents a pressureless fluid discharge and contains an overflow throttle.
A leakage of hydraulic fluid from the closed hydraulic circuit is unavoidable during long periods of operation. The lost hydraulic fluid is slowly replaced with an air bubble without special measures, which because of the compressibility of air can cause initial control delays and when continuing can result in machining inexactnesses and breakdowns in operation. To avoid this, a preferred embodiment of the invention provides that the lost hydraulic fluid is constantly automatically replenished. A fluid reservoir is arranged in the supporting body for this purpose, through which reservoir hydraulic fluid is automatically added to the hydraulic circuit. The fluid reservoir is advantageously designed as a piston cylinder connected to the hydraulic circuit through a check valve and the piston of which acts under initial biassing against the fluid contained in the cylinder. The piston rests advantageously under the action of a spring against the fluid column. Furthermore, the piston can be arranged such that it acts, with the spindle rotating, under the action of the centrifugal force, onto the fluid column. The latter is the case when the piston rests radially outwardly against the fluid column, in particular when it is arranged radially within the fluid column in the fluid reservoir.
A fill-level control in the fluid reservoir and thus in the closed hydraulic circuit is realized according to the invention by rigidly connecting a pin to the piston, which pin upon a fluid reduction is moved radially outwardly in a pin hole. The pin hole can be arranged essentially radially in a locking lid of the fluid reservoir. When the control pin in the pin hole reaches the outer contour of the housing, then this is proof that fluid must be added. The fluid reservoir can for this purpose be filled from outside with hydraulic fluid through a closeable fill opening.
According to a further advantageous embodiment of the invention, the diameter of the first chamber is larger than the one of the chamber cylinder. The supporting body has advantageously a stepped bore concentric with respect to the axis of rotation, which bore is divided into two chambers by an intermediate lid connected to the bore step and having a fluid-tight, sealed piston-rod through opening therein. When the supporting body has a steep-angle taper shaft, then at least the second chamber and the return spring are arranged within the steep-angle taper shaft. The tool shaft can thereby have an annular recess opening toward the second chamber concentric with respect to the axis of rotation to receive the return spring in the form of a compression spring.
The piston in the second chamber has advantageously a further piston rod extending toward the spindle on a side remote from the first chamber, which piston rod sealingly, slidingly extends into a fluid chamber connectable to the connecting opening for the pressure fluid, which connecting opening is on the side of the spindle, so that the coolant channel leading to the first chamber and the head element can be extended axially through the piston rod and the further piston rod. In order to obtain a type of construction of the supporting body which is compact in axial direction, the supporting body has a bore concentric with respect to the axis of rotation with a cup-shaped piston therein which is open on one side to form the second chamber, and defining with a bottom wall thereof the first chamber within the bore, which wall has a piston-rod through opening therethrough. The bottom wall of the cup-shaped piston has advantageously an annular recess opening toward the first chamber to receive an annular shoulder axially projecting from the first piston and having at least one peripheral groove to receive a guide and/or seal ring therein.